Results 1 - 10 of 1710
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[en] During the first 7 yr of the INTEGRAL mission (2003-2009), Cyg X-1 has essentially been detected in its hard state (HS), with some incursions in intermediate HSs. This long, spectrally stable period allowed in particular the measurement of the polarization of the high-energy component that has long been observed above 200 keV in this peculiar object. This result strongly suggests that here we see the contribution of the jet, known to emit a strong synchrotron radio emission. In 2010 June, Cyg X-1 underwent a completed transition toward a soft state (SS). It gave us the unique opportunity to study in detail the corona emission in this spectral state, and to investigate in particular the behavior of the jet contribution. Indeed, during the SS, the hard X-ray emission decreases drastically, with its maximum energy shifted toward lower energy and its flux divided by a factor of ∼5-10. Interestingly, the radio emission follows a similar drop, supporting the correlation between the jet emission and the hard component, even though the flux is too low to quantify the polarization characteristics.
[en] We report on the first analysis of an AstroSat observation of the Z-source GX 5–1 on 2017 February 26−27. The hardness-intensity plot reveals that the source traced out the horizontal and normal branches. The 0.8−20 keV spectra from simultaneous SXT and LAXPC data at different locations of the hardness-intensity plot can be described well by disk emission and a thermal Comptonized component. The ratio of the disk flux to the total flux, i.e., the disk flux ratio, increases monotonically along the horizontal branch to the normal one. Thus, the difference between the normal and horizontal branches is that in the normal branch, the disk dominates the flux while in the horizontal one it is the Comptonized component which dominates. The disk flux scales with the inner disk temperature as and not as , suggesting that either the inner radius changes dramatically or that the disk is irradiated by the thermal component changing its hardness factor. The power spectra reveal a quasi-periodic oscillation (QPO) whose frequency changes from ∼30 Hz to 50 Hz. The frequency is found to correlate well with the disk flux ratio. In the 3−20 keV LAXPC band, the r.m.s. of the QPO increases with energy (r.m.s. ), while the harder X-rays seem to lag the soft ones with a time-delay of milliseconds. The results suggest that the spectral properties of the source are characterized by the disk flux ratio and that the QPO has its origin in the corona producing the thermal Comptonized component. (paper)
[en] We study the issue of active galactic nucleus (AGN) and host co-evolution by focusing on the correlation between the hard X-ray emission from central AGNs and the stellar populations of the host galaxies. Focusing on galaxies with strong Hα line emission (EW(Hα) > 5 Å), both X-ray and optical spectral analyses are performed on 67 (partially) obscured AGNs that are selected from the XMM-Newton 2XMMi/SDSS-DR7 catalog originally cross-matched by Pineau et al. The sample allows us to study central AGN activity and host galaxy activity directly and simultaneously in individual objects. Combining the spectral analysis in both bands reveals that the older the stellar population of the host galaxy, the harder the X-ray emission will be, which was missed in our previous study where ROSAT hardness ratios were used. By excluding the contamination from host galaxies and from jet beaming emission, the correlation indicates that Compton cooling in the accretion disk corona decreases with the mean age of the stellar population. We argue that this correlation is related to the correlation of L/LEdd with the host stellar population. In addition, the [O I]/Hα and [S II]/Hα narrow-line ratios are identified to correlate with the spectral slope in hard X-rays, which can be inferred from the currently proposed evolution of the X-ray emission because of the confirmed tight correlations between the two line ratios and stellar population age.
[en] The bright type I Seyfert galaxy NGC 3516 was observed by Suzaku twice, in 2005 October 12-15 and 2009 October 28-November 2, for a gross time coverage of 242 and 544 ks and a net exposure of 134 and 255 ks, respectively. The 2-10 keV luminosity was 2.8 × 1041 erg s–1 in 2005 and 1.6 × 1041 erg s–1 in 2009. The 1.4-1.7 keV and 1.7-10 keV count rates both exhibited peak-to-peak variations of a factor of ∼2 in 2005 and ∼4 in 2009. In both observations, the 15-45 keV count rate was less variable. The 2-10 keV spectrum in 2005 was significantly more convex than that in 2009. Through a count-count plot technique, the 2-45 keV signals in both sets of data were successfully decomposed in a model-independent way into two distinct broadband components. One is a variable emission with a featureless spectral shape, and the other is a non-varying hard component accompanied by a prominent Fe-K emission line at 6.33 keV (6.40 keV in the rest frame). The former was successfully fitted by an absorbed power-law model, while the latter requires a new hard continuum in addition to a reflection component from distant materials. The spectral and variability differences between the two observations are mainly attributed to long-term changes of this new hard continuum, which was stable on timescales of several hundreds of kiloseconds.
[en] We report the discovery of kiloparsec-scale diffuse emission in both the hard continuum (3–6 keV) and in the Fe–Kα line in the Compton thick (CT) Seyfert galaxy ESO 428-G014. This extended hard component contains at least ∼24% of the observed 3–8 keV emission, and follows the direction of the extended optical line emission (ionization cone) and radio jet. The extended hard component has ∼0.5% of the intrinsic 2–10 keV luminosity within the bi-cones. A uniform scattering medium of density would produce this luminosity in a 1 kpc path length in the bi-cones. Alternatively, higher column density molecular clouds in the disk of ESO 428-G014 may be responsible for these components. The continuum may also be enhanced by the acceleration of charged particles in the radio jet. The steeper spectrum (Γ ∼ 1.7 ± 0.4) of the hard continuum outside of the central 1.″5 radius nuclear region suggests a contribution of scattered/fluorescent intrinsic Seyfert emission. Ultrafast nuclear outflows cannot explain the extended Fe–Kα emission. This discovery suggests that we may need to revise the picture at the base of our interpretation of CT AGN spectra.
[en] We report on high-resolution optical and hard X-ray observations of solar flare ribbons seen during the GOES X6.5 class white-light flare of 2006 December 6. The data consist of imaging observations at 430 nm (the Fraunhofer G band) taken by the Hinode Solar Optical Telescope with the hard X-rays observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager. The two sets of data show closely similar ribbon structures, strongly suggesting that the flare emissions in white light and in hard X-rays have physically linked emission mechanisms. While the source structure along the ribbons is resolved at both wavelengths (length ∼ 30''), only the G-band observations resolve the width of the ribbon, with values between ∼0.''5 and ∼1.''8. The unresolved hard X-ray observations reveal an even narrower ribbon in hard X-rays (the main footpoint has a width perpendicular to the ribbon of <1.''1 compared to the G-band width of ∼1.''8) suggesting that the hard X-ray emission comes from the sharp leading edge of the G-band ribbon. Applying the thick-target beam model, the derived energy deposition rate is >5 x 1012 erg s-1 cm-2 provided by an electron flux of 1 x 1020 electrons s-1 cm-2 above 18 keV. This requires that the beam density of electrons above 18 keV be at least 1 x 1010 cm-3. Even if field lines converge toward the chromospheric footpoints, the required beam in the corona has too high a density to be described as a dilute tail population on top of a Maxwellian core. We discuss this issue and others associated with this extreme event, which poses serious questions to the standard thick target beam interpretation of solar flares.
[en] The black hole binary GS 2023+338 exhibited an unprecedently bright outburst in 2015 June. On 2015 June 17, the high energy instruments on board INTEGRAL detected an extremely variable emission during both bright and low luminosity phases, with dramatic variations of the hardness ratio on timescales of approximately seconds. The analysis of the IBIS and SPI data reveals the presence of hard spectra in the brightest phases, compatible with thermal Comptonization with a temperature of kT_e ∼ 40 keV. The seed photon’s temperature is best fit by kT_0 ∼ 7 keV, which is too high to be compatible with blackbody emission from the disk. This result is consistent with the seed photons being provided by a different source, which we hypothesize to be a synchrotron driven component in the jet. During the brightest phase of flares, the hardness shows a complex pattern of correlation with flux, with the maximum energy released in the range of 40–100 keV. The hard-X-ray variability for E > 50 keV is correlated with flux variations in the softer band, showing that the overall source variability cannot originate entirely from absorption, but at least part of it is due to the central accreting source
[en] A multipurpose experiment including search for periodic hard X-ray sources (10-200 keV) was carried out from the 1st of Jule, 1983 to the 14th of February, 1984 on a high apogee (720,000 km) ''Prognoz-9'' with a set of instruments containing an X-ray device and background charged particle monitors. Due to the large field of view and constant pointing of the X-ray device to the Sun during the experiment a slow scan of a wide strip of sky (+50 deg from eliptic) was performed. During passing the Galactic center region variations of galactic emission of different types were detected. The epoch folding method enabled to distinguish periodic processes known (82h-1700-37) as well as not observed before (62h, 67h, 98h, 152h)
[en] We observed the soft gamma repeater SGR 0501+4516 with Suzaku for ∼51 ks on 2008 August 26-27, about 4 days after its discovery. Following the first paper, which reported on the persistent soft X-ray emission and the wide-band spectrum of an intense short burst, this paper presents an analysis of the persistent broadband (1-70 keV) spectra of this source in outburst, taken with the X-ray Imaging Spectrometer (XIS) and the Hard X-ray Detector (HXD). Pulse-phase folding in the 12-35 keV HXD-PIN data on an ephemeris based on multi-satellite timing measurements at soft X-rays revealed the pulsed signals at ∼>99% confidence in the hard X-ray band. The wide-band spectrum clearly consists of a soft component and a separate hard component, crossing over at ∼7 keV. When the soft component is modeled by a blackbody plus a Comptonized blackbody, the hard component exhibits a 20-100 keV flux of 4.8+0.8-0.6(stat.)+0.8-0.4(sys.) x 10-11 erg s-1 cm-2 and a photon index of Γ = 0.79+0.20-0.18(stat.)+0.01-0.06(sys.). The hard X-ray data are compared with those obtained by INTEGRAL about 1 day later. Combining the present results with those on other magnetars, we discuss a possible correlation between the spectral hardness of magnetars and their characteristic age and magnetic field strengths.